Actually, brackets are taxable as misc income, but that does not make them gambling. My bracket money gets reported to me on the same line as my other winnings from USBC and megabuck tourneys. I file a Schedule C tax return listing bowling as my profession. I am allowed to take all appropriate business deductions including entry fees against the bracket and/or regular tourney winnings. I can only show net losses under very narrow circumstances, but anyone may attach a schedule C taking the position that bowling is a hobby which does allow you to offset entry fees. One word of warning however. You are required to pay self employment on your net income under this scenario. Finally, don't blame the USBC. The IRS started requiring them to report gross prizes quite a few years ago, and they are not allowed to report your winnings net of entry fees.
Life is a gamble, so under that term brackets are gambling, but under most state law definitions that I am familiar with they would escape the legal term of gambling because the player has enough control over the outcome to take them out of the gambling category.
Brunswick has the right to not allow brackets in their houses, but the gambling rationale is either an ignorant position, or a convenient excuse.